Catheterization of the carotid artery and the jugular vein is one of the most commonly applied techniques used to gain intravascular access in pharmacology studies on rodents. We catheterized 10 rats by conventional clean techniques, 10 rats by aseptic techniques and 10 rats by conventional clean techniques using a heparin-coated catheter rather than an ordinary non-coated polyvinyl chloride catheter. In all groups, approximately 80% of the rats developed kidney infection and 10-30% of the rats were septicaemic. Clinical chemistry did not indicate severe kidney damage, but serum haptoglobin and body temperature rises indicated an inflammatory response in rats independent of the surgical method. Heparin coating did not seem to improve the usability of the catheter. It is concluded that this commonly used method for catheterization has an impact on animals that may very well render them unsuitable for the purpose, e.g. pharmacological research, and therefore an alternative method would be preferable.